The present invention relates to process and apparatus for detecting leaks in and/or cathodically protecting an aboveground fluid storage tank, and more particularly, to process and apparatus for detecting leaks across and cathodically protecting substantially the entire bottom surface of an aboveground fluid storage tank while permitting access to the area below the bottom surface of a storage tank should remediation of the ground below the storage tank and/or recovery of a leaked fluid be required.
Fluids and products, such as water, crude oil, refined petroleum products, petrochemicals, or chemicals are conventionally stored for transportation and/or further processing in aboveground, stationary storage tanks, vessels, or containers. These conventional storage tanks are generally cylindrical in configuration. The bottom of these storage tanks is in contact with the ground upon which the tank is positioned. Tank(s) may be juxtaposed to a producing oil well or a pipeline terminal in the field to storage produced liquid hydrocarbons for transportation to a refinery or a plurality of tanks may be present at a refinery to store both crude oil and refined petroleum products. Tens of thousands of such conventional aboveground storage tanks have been previously constructed and installed and have been in service for many years. Substantially all of these storage tanks are constructed of metal, such as steel alloys.
Metallic containers positioned upon and/or partially within the ground are subject to failure due to a variety of corrosion processes that affect both the internal and external surfaces of the tank bottom. Given time, metallic, aboveground storage tanks will develop fluid leaks due to corrosion of the bottom surface thereby releasing water, crude oil, refined petroleum products, petrochemicals, and/or chemicals into the ground below the storage tank. If undetected and unmonitored, fluid leaks from an aboveground storage tank will contaminate the ground, soil and/or rock below the tank(s) as well as underlying aquifers.
Thus, considerable attention has been directed to cathodically protecting aboveground storage tanks in addition to monitoring such storage tanks to determine if fluid is leaking or has leaked from such tanks. Where the tank bottom is of a relatively small diameter and where the aboveground storage tank is effectively isolated from other aboveground and underground metallic structures so that current requirements for cathodic protection are small, aboveground storage tanks have been cathodically protected by the use of sacrificial anodes positioned within the ground about the periphery of the storage tank. Where current requirements are significant, impressed current systems have been installed to cathodically protect aboveground storage tanks. Anodes for impressed current systems have conventionally been installed in one of two manners. First, impressed current anodes have been installed in deep well or remote ground bed configurations which may be remote from the storage tank. Deep well designs involve placement of anodes in generally vertical bores at depths of 100 feet or more. Secondly, impressed current anodes have been installed at relatively shallow depths about the periphery of the tank either juxtaposed to the tank perimeter or at a site which is distant from the tank. Electrical current from such impressed current systems is largely consumed within the perimeter areas of the tank bottom. Thus, corrosion protection decreases from periphery of the tank bottom to the center. In an attempt to compensate for the deficiencies of these impressed current systems, electrical current to such systems has been significantly increased. However, increased current has resulted in excessive total current output and operating costs and stray current interference problems.
Procedures and equipment for volumetric testing, inventory reconciliation, and acoustic emissions testing have been developed and physical tank bottom inspections have been conducted from within the tank to either determine the existence of a leak or measure the amount of a fluid discharged through a leak in an aboveground tank bottom. However, none of these procedures, equipment, or inspections assess the actual conditions within the ground below the tank bottom, nor have they proved to be economical or capable of determining low volumes of fluid loss. Thus, a need exists for process and apparatus for cathodically protecting substantially the entire bottom of an aboveground storage tank for economically, timely and accurately detecting fluid leaks from an aboveground storage tank and for providing access to the area below the bottom of an aboveground storage tank for soil remediation, to contain a leaked fluid, and to prevent further migration of the leaked fluid in situ.
Accordingly, it is an object of the present invention to provide a process and apparatus for cathodically protecting substantially the entire bottom of an aboveground storage tank.
It is another object of the present invention to provide a process and apparatus for monitoring substantially the entire area below an aboveground storage tank for the existence of a fluid tank.
It is also an object of the present invention to provide apparatus which will allow contaminated ground, soil, and/or rock below an aboveground storage tank to be remediated and/or inhibit migration of a fluid which has leaked from an aboveground storage tank.
It is a further object of the present invention to position a perforated or slotted pipe or casing under an aboveground storage tank to be used for the determination of accurate structure-to-soil potentials so as to define the effectiveness of a cathodic protection system.
It is also a further object of the present invention to provide a process and apparatus for simultaneously boring and casing a generally horizontal subterranean bore.
It is a still further object of the present invention to provide portable apparatus for accurately obtaining structure-to-soil potential measurements from any location within perforated or slotted pipe which is positioned below an aboveground storage tank.